1. Field of the Invention
The present invention relates to a plasma processing apparatus and processing method, particularly to a plasma processing apparatus and processing method suitable for formation of ultrafine pattern in semiconductor production process.
2. Related Background Art
In semiconductor production process, a plasma processing apparatus is widely used in fine processing such as etching, film formation and ashing. In plasma processing, process gas introduced into a vacuum chamber (reactor) is converted to plasma by a plasma generation means, and is made to react on the semiconductor wafer surface to provide fine processing, and volatile reaction products are exhausted, thus a predetermined process is performed.
This plasma processing is strongly affected by temperature of the reactor inner wall and wafer and deposition of reaction products on the inner wall. Furthermore, if the reaction products deposited inside the reactor have peeled off, partilcle may be produced, resulting in deterioration of device characteristics or reduction of yields. In the plasma processing apparatus, therefore, it is important to control temperature inside the reactor and deposition of reaction products on the surface, in order to ensure process stability and to prevent particle contamination.
For example, Official Gazette of Japanese Patent Laid-Open NO. 144072/1996 discloses a dry etching apparatus which controls and maintains the temperature of each part inside the reactor to a high temperature of 150 to 300xc2x0 C. (preferably 200 to 250xc2x0 C.), at least 150xc2x0 C. higher than that of etching stage, within the accuracy of xc2x15xc2x0 C., wherein the purpose is to improve the selectivity in a silicon oxide dry etching process. This is intended to reduce deposition of plasma polymer on the inner wall of the reactor by controlling each part inside the reactor to high temperature, thereby increase the deposition of plasma polymer on the semiconductor wafer, with the result of improved selectivity.
Also, Official Gazette of Japanese Patent Laid-Open NO. 275385/1993 discloses a parallel plate plasma processing apparatus wherein a heating means is provided on at least one of a clamp ring (object holding means) or focus ring (plasma concentration means) to raise and keep the temperature in order to prevent deposition of plasma process reaction products. As a heating means, a resistance heater is used. Since deposition of reaction products can be prevented by heating, peeling off of reaction products and particles on the object surface are reduced.
However, when the reactor inner wall is set to a high temperature of 200 to 250xc2x0 C. or more as described above, a problem arises that etching characteristics becomes very sensitive to the temperature of the inner wall surface, and repeatability and reliability of the process can be reduced.
For example, S. C. McNevin, et al., J. Vac. Sci. Technol. B15(2) March/April 1997, P.21, xe2x80x9cChemical challenge of submicron oxide etchingxe2x80x9d indicates that oxide film etching rate increases 5% or more, in the inductively coupled plasma when side wall temperature changes from 200 to 170xc2x0 C., therefore, surface temperature inside the reactor is required to be kept to a high accuracy of 250 xc2x12xc2x0 C. in order to ensure stability of process characteristics.
Furthermore, since the surface of the processing chamber inner wall is exposed to high density plasma, it is not easy to control the wall surface temperature with high accuracy in the high temperature range. A highly accurate in-situ temperature measuring means and a heating means such as resistance heater or lamp are to be used for temperature control. However, the temperature control mechanism and means will be quite complicated and large in scale, resulting in complicated equipment with high cost. In a high temperature range of more than 200xc2x0 C., another problem exists that the materials applicable for the inner wall are limited.
In this respect, the present applicants discloses in the Japanese Patent Application No. 147672/1998 (Official Gazette of Japanese Patent Laid-Open NO. 340149/1999) by the same applicants that the process can be insensitive to temperature changes and stable process repeatability can be ensured despite the temperature accuracy of about xc2x110xc2x0 C., when the temperature of the processing chamber inner wall is set to the temperature range of lower than 100xc2x0 C., wherein said applicants use a magnetic field UHF band electromagnetic wave radiation discharge type plasma etching apparatus as one Embodiment.
The same application discloses that, by applying bias at least partly to the components (or inner wall surface) in contact with plasma, and by reducing the thermal capacity of the components to keep component temperature in the range from 150 to 250xc2x0 C., it is possible to come to the level that the temperature fluctuation of components does not affect the process substantially.
The present applicants in the Japanese Patent Application No. 232132/1999 by the same applicants also disclose that, when higher bias power of no deposition occurrence is applied to the silicon-made focus ring set outside the sample, and when the surface temperature is higher than 150xc2x0 C., surface reaction dependency upon temperature on the silicon surface is reduced and stable process repeatability can be ensured.
However, as for the plate installed on the top antenna (or upper electrode or top plate) opposite to the sample wafer, although the plate has a big influence on process stability, said application only states that the plate has a role of stabilizing the process by preventing reaction product from deposition by application of bias, and said applicants did not reach sufficient understanding of the mechanism nor succeed in quantifying the required conditions.
From said technological standpoint, the present inventors made a strenuous effort to solve said problems, and found out temperature range and accuracy required to ensure process stability and requirements for surface state control by bias application, regarding the top plate installed opposite to the sample wafer.
The present invention was developed on the basis of the aforementioned findings, and is intended to provide a plasma processing apparatus and processing method with excellent process stability and repeatability.
The present invention provides a plasma processing apparatus comprising; a vacuum chamber, a process gas supply means to supply gas to said vacuum chamber, an electrode to hold a sample inside said vacuum chamber, a plasma generator installed in said vacuum chamber opposite to said sample, and a vacuum exhaust system to evacuate said vacuum chamber;
wherein said plasma generator is installed a silicon-made plate inside the processing chamber, and bias voltage of Vdc=xe2x88x9250 to xe2x88x92300 V (i.e. xe2x88x92300 Vxe2x89xa6Vdcxe2x89xa6xe2x88x9250 V) is applied to said silicon-made plate, and the surface temperature of said plate is kept in the range from 100 to 200xc2x0 C.
Another characteristic of the present invention is that the fluctuation of the surface temperature of the silicon-made plate on said plasma processing apparatus is kept within xc2x125xc2x0 C.
Still further characteristic of the present invention is that said plasma generator of plasma processing apparatus is based on magnetic field or non-magnetic field UHF band electromagnetic wave radiation discharge method in the frequency range from 300 MHz to 1 GHz, and that the resistivity of said silicon-made plate is 1 to 10 xcexa9cm, and that the thickness of said silicon-made plate is 5 to 20 mm, desirably up to 10 mm.
According to the present invention, dependency of reaction on temperature on the silicon surface decreases by temperature control and bias application for silicon-made plate installed opposite to the sample and plasma state and process characteristics are stabilized for surface temperature fluctuation of the plate within xc2x125xc2x0 C., thus a plasma processing apparatus and processing method with excellent stability and repeatability can be provided.
The present invention is still further characterized as follows: the skin depth of the UHF band electromagnetic wave transmitting inside the silicon-made plate and silicon plate thickness are almost equal, and current resulting from UHF band electromagnetic wave flows the entire plate. As a result, the plate is effectively heated by self-heat generation due to the internal resistance of silicon itself, which enables to set surface temperature of the silicon-made plate in the range from 100 to 200xc2x0 C. where dependency of surface reaction on temperature decreases. As a result plasma state and process characteristics are stabilized, thus a plasma processing apparatus and processing method with excellent stability and repeatability can be provided.